Air conditioning compressors are known in the art, such as from DE 10 2011 117 354 A1, for example. Pistons are arranged in a crank casing of the air conditioning compressor in order to pump refrigerant into a pressure chamber. In the process, the movement of the pistons is guided by a rotating wobble plate. If the wobble plate, which is rotated via a belt drive, for example, has a tilt angle different from zero, this leads to an axial stroke movement of the pistons as they turn around the wobble plate's axis of rotation. In the process, refrigerant is sucked up by the suction chamber of the air conditioning compressor and pumped into the pressure chamber.
The known air conditioning compressor is mounted in a motor vehicle. The suction chamber is connected to the low-pressure-side connector of the air conditioning compressor, which is connected to the low-pressure area of the air conditioning system, such as the condenser's outlet. The pressure chamber is connected to the high-pressure-side outlet of the air conditioning compressor, which is connected to the high-pressure area of the climate system, such as a heat exchanger with the inlet of the condenser.
To adapt the displacement volume and control the flow of refrigerant, varying the tilt angle of the wobble plate in the air conditioning compressor is already known. For example, if the air conditioning compressor is preset for a maximum displacement volume, a pivoting back of the wobble plate brings about a decrease in the axial hub stroke of the pistons and thus a reduction of the displacement volume.
Furthermore, controlling the refrigerant flow by a control valve is also known. The control valve is connected to the high-pressure area, the low pressure area and the crankcase pressure area and controls the flow of refrigerant between the three areas. If the control valve, in one position, opens a connection between the high-pressure area and crankcase pressure area, refrigerant flows from the high-pressure area into the crankcase pressure area; there is a pressure rise in the crankcase pressure area. If the control valve, in another position, opens a connection between the crankcase pressure area and the low-pressure area of the air conditioning compressor, refrigerant flows from the crankcase pressure area into the low-pressure area; there is a pressure fall in the crankcase pressure area.
The pressure rise in the crankcase pressure area controlled by the control valve brings about a pivoting back of the wobble plate. Thus, the axial stroke movement of the air conditioning compressor's pistons decreases and the displacement volume of the air conditioning compressor is reduced. Consequently, the pressure does not increase further in the high-pressure area of the air conditioning system. The pressure fall in the crankcase pressure area controlled by control valve brings about a swinging out (i.e. tipping) of the wobble plate. Thus the axial stroke movement of the air conditioning compressor's pistons increases and the displacement volume of the air conditioning compressor is made larger. Consequently, the pressure increases further in the high-pressure area of the air conditioning system. Usually, the wobble plate is held in the tipped starting position by spring tension, so that if there is a later fall in pressure in the crankcase pressure area the wobble plate pivots into the starting position again and provides a starting position with regard to the displacement volume in the air conditioning compressor.
A control valve 100 known in the art and used for an air conditioning compressor to control a refrigerant flow from a high-pressure area into a crankcase pressure area, and from the crankcase pressure area into a low-pressure area, is shown in FIG. 1. Actuation of the control valve 100 takes place through the movement of a control piston 104. The control piston 104 comprises an actuation rod 106 with at least one seal body 108. The actuation rod 106 moves in and in opposition to the longitudinal direction of the control piston 104, so that the seal body 108 respectively opens or blocks the passage between a high-pressure area Pd and a crankcase area Pc in the control valve 100.
The movement of the control piston 104 is guided by a longitudinal bore in the casing of the control valve 100. Furthermore, lateral recesses Ps, Pd and Pc are provided in the casing for the connection of the high-pressure area Pd, the low-pressure area Ps, and the crankcase pressure area Pc. The seal body 108 is conical to cooperate with an annular inlet/outlet aperture in the passage between the high-pressure area Pd and the crankcase pressure area Pc and in the passage between the crankcase pressure area Pc and the low-pressure area Ps.
If the control piston 104 is moved into a first position, the seal body 108 opens the passage from the high-pressure area Pd into the crankcase pressure area Pc. At the same time, the passage between the crankcase pressure area Pc and the low-pressure area Ps is sealed. Consequently, refrigerant can flow from the high-pressure area Pd into the crankcase pressure area Pc and can provide a rise in pressure there. The first position of the control valve 100 results in the air conditioning compressor being regulated downwards.
If the control piston 104 is moved into a second position, the seal body 108 opens the passage between the crankcase pressure area Pc and the low-pressure area Ps. At the same time, the passage between the high-pressure area Pd and the crankcase pressure area Pc is sealed. Consequently, refrigerant will flow from the crankcase pressure area Pc into the low-pressure area Ps and provide a fall in pressure in the crankcase pressure area Pc. The second position of the control valve 100 results in the air conditioning compressor being regulated up.
The movement of the control piston 104 is brought about by an electromagnetic annular coil 102 arranged to the side of the actuation rod 106. If power is fed into the annular coil 102, there is induced in the interior of the coil a magnetic field which interacts with the end of the actuation rod 106 of the control piston 104 arranged inside the annular coil. The end of the actuation rod 106 of the control piston 104 arranged inside the annular coil 102 is made of ferromagnetic material.
In control valves 100 operated with an electromagnetic annular coil 102, however, control of the movement of the control piston 104 between the first and the second position is imprecise. The mechanical and magnetic interactions between the annular coil 102 and the end of the actuation rod 106 of the control piston 104 arranged therein result in a hysteresis in the movement of the control piston 104 with regard to the power fed into the annular coil 102. Furthermore, the high and low pressures respectively acting on the seal body 108 in the high-pressure area Pd and the low-pressure area Ps are variable and counteract the induced magnetic field. Thus, by way of example, in the event of a higher pressure in the high-pressure area Pd, a stronger magnetic field is required, for example to move the control piston 104 from one position into the second. Furthermore, precise control of the control valve 100 is difficult due to the complicated nature of ascertaining the location of the control piston 104 and is not energy efficient, for example, because a constant flow of current in the electromagnetic annular coil 102 is necessary even to keep the control piston 104 in the closed position.